1. Field of the Invention
The present invention relates to a method of cooling devices accommodated within a hermetically closed control box or cabinet. The invention also concerns an apparatus for carrying out the method.
In the course of remarkable progress and diversification of electronic devices or apparatus, there arises increasingly the demand for a hermetic type control box (i.e. hermetically closed box) which can protect electronic devices or apparatus accommodated therein from environmental influences such as dust, water and corroding action of ambient gases. In this conjunction, providing such a control box is made difficult by the problem of temperature rise within the closed box caused by heat generation of the electronic devices or apparatus.
The present invention concerns the cooling for a hermetic type control box and in particular a method and apparatus for controlling the cooling of a hermetic type control box incorporating a cooling system.
2. Description of the Prior Art
Heretofore, several attempts have been proposed concerning heat dissipation of a hermetic type control box.
One of them resides in a heat conducting method according to which a material having a high thermal conductivity is made use of for conducting heat from a heat generating portion to a heat sink for dissipation. This method is certainly very convenient and adopted in many practical applications. However, it suffers a disadvantage that restrictions are inevitably imposed on the package of the electronic devices and the structure of the control box when a satisfactory thermal conduction is to be realized, involving a complicated structure of the whole equipment and much time for manufacturing.
In another proposal which seems to solve the above problem a fan is mounted within the hermetic type control box, whereby heat generated by the electronic devices is carried away by air flow produced by the fan. The air flow is directed perpendicularly to the inner wall of the box so as to be recirculated within the box by the fan. Although this solution eliminates the need for the heat conducting material, the cooling action cannot be satisfactorily attained when the ambient temperature is high. Further, heat generation by the fan itself can not be neglected. When the ambient temperature rises, for example, beyond 30.degree. C. in mid summer, the permissible temperature rise of the electronic devices is correspondingly limited, to a disadvantage.
As another attempt for cooling a hermetic type control box, it has been proposed to effect heat exchange between the interior of the box where the electronic devices are housed and the surroundings, to thereby cause the air cooled by the ambient atmosphere to circulate within the hermetically closed box where the electronic devices are accommodated. Reference may be made to Japanese Patent Publication No. 19758/81, published May 9, 1981. However, the cooling effect also depends on the ambient temperature as is in the case of the aforementioned proposal. In other words, this proposal does not solve the problem that the permissible temperature rise of the electronic devices is reduced when the ambient temperature is high, thereby restricting the packaging density of the electronic devices within the box.
As other approaches, it is conceivable to make use of the Peltier effect or immerse the electronic devices in an insulation coolant such as, for example, in a bath of insulation oil as adopted in oil-filled transformers. However, at present, these cooling systems are not yet widely adopted in the field of the hermetic type control box. In the former case, a power source of a relatively large capacity will be required, while the structure of the box or housing is considerably complicated in the latter case, giving rise to another problem.